Process of copper plating super-refined steel

ABSTRACT

A process for the currentless copper plating of super refined steel wherein the steel is contacted with a solution containing copper, hydrogen and fluoride ions, but no inhibitors, to produce, through cementation, a copper coating on the steel. The concentration of the fluoride ions and hydrogen ions in the plating solution are maintained within specified, varying ranges, depending upon the temperature at which the coating bath is operated. In this manner, a currentless copper coating is produced on super-refined steel, which steel has not heretofore been coatable in this manner.

United States Patent [72] Inventors Han Yong Oei;

Siegfried Moller, both of Frankport, Main, Germany [21] Appl. No. 778,117 [22] Filed Nov. 22, 1968 [45] Patented Nov. 16, 1971 [73] Assignee Hooker Chemical Corporation Niagara Falls, N.Y.

[54] PROCESS OF COPPER PLA'IlNG SUPER-REFINE!) STEEL 5 Claims, 1 Drawing Fig.

[52] U.S.Cl 117/130 R, 106/1, 117/128 [51] Int. Cl C23c 3/00 [50] Field of Search... 117/130, 130 E, 130 B; 106/1; 156/18 [56] References Cited UNITED STATES PATENTS 2,111,199 3/1938 Alvord 117/130 2,217,921 10/1940 Saukaitis 106/1 2,410,844 1ll1946 Signaigo et a1 117/130 2,445,372 7/1948 Trenbath 1 17/130 X 2,472,393 6/1949 Avallone et al. 1 17/130 2,814,589 11/1957 Waltz 106/1 X 2,825,682 3/1958 Missel et al. 106/] X 3,280,038 10/1966 Morris 156/18 X OTHER REFERENCES Metals Handbook, Ohio, American Society of Metals, 1948, p. 557. 156- 18 Primary Examiner-Alfred L. Leavitt Assistant Examiner.l. R. Batten, Jr. AttorneysStanley H. Lieberstein and William J. Schramm less copper coating is produced on super-refined steel, which steel has not heretofore been coatable in this manner.

PROCESS OF COPPER PLATING SUPER-REFINED STEEL This invention relates to a process for the currentless copper plating of ferrous metal, and more particularly it relates to a method for the currentless copper plating of superrefined steel through cementation by treatment with an aqueous, acidic copper solution.

lt is known in the art that the copper plating of iron and other ferrous alloys can be obtained without current by the use of an aqueous acidic solution which contains copper ions. Notwithstanding this, however, appreciable difficulties have been encountered in obtaining a satisfactory and adherent copper coating by this method, particularly where the ferrous surface is a super refined steel. Accordingly, a great number of modifications have been proposed for the copper coating solutions to improve the quality of the plating obtained, which modifications have involved the use of various modifying agents or inhibitors in the coating bath.

In one prior art process, it has been proposed to use organic inhibitors which will suppress the dissolution of iron in the coating bath. These inhibitors are added to a copper plating solution which contains fluoride, bromide, or chloride ions, in addition to hydrogen ions, and include various coal-tar bases, bases extracted from distillation products, aldehyde-amine reaction products, aldehyde-ketone reaction products, various amino-acids, alkaloids, such as quinine, quinoidine, sulfated derivatives of these, and the like. In another process, polyhydroxy thiols are proposed as inhibitors while another process proposes the use of ethoxylated long chain aliphatic amines as modifying materials.

In another process, it is proposed that in order to increase the surface gloss and decrease the surface grain size of the copper plating, the following may be used as inhibitors: condensation products of adipic alcohols, adipic acids, tall oil, alkyl phenolene, adipic amines, ethylene oxide substituted thio-uric acids; long chain organic amines; reducing sugars; decomposition products of sugar; quaternary ammonium salts, such as, laurylpyredinium sulfate; aryl sulfides and sulfoxides. In yet another prior process, it is proposed to add acridine and various acridine derivatives as inhibitors or modifying agents for a currentless copper plating bath which is an aqueous acidic solution containing copper ions and chloride ions.

in spite of the numerous processes and solutions which have heretofore been proposed, none of these have produced a satisfactory copper plating on super-refined steel. Although the reason for the failure of these solutions to coat this material is not known for certain, it is believed that the passivity of super refined steel may be the cause. This passivity is believed to prevent the exchange reaction from taking place between iron and copper. For whatever the reason, however, the presently known processes and solutions for currentless copper plating have not produced a satisfactory copper coating on such super-refined steel surfaces.

It is, therefore, an object of the present invention to provide an improved process for the currentless copper plating of ferrous metal surfaces.

A further object of the present invention is to provide an improved currentless copper plating process, which process is capable of forming a satisfactory copper coating on superrefined steel surfaces.

These and other objects will become apparent to those skilled in the art from the description of the invention which follows.

The drawing is a phase diagram illustrating the concentration ranges for various bath components at several temperatures.

Pursuant to the above objects, the present invention includes a process for producing a copper plating on ferrous metal, without the use of current, which process comprises contacting the ferrous metal surface with an aqueous acidic solution containing copper ions, hydrogen ions, and fluoride ions, which solution is free of inhibitors, and maintaining the solution in contact with the ferrous surface until the desired copper coating is obtained, wherein the concentration of the fluoride ions is maintained within the limits denoted by the following coordinates depending upon the solution temperature:

20' C. 0.l to 4 moles per liter 35 C. 0.l to 2.8 moles per liter 50 C. 0.] to 1.3 mole: per liter 55 C. 0.1 to 0.8 moles per liter and the hydrogen ion concentration is maintained within the limits denoted by the following coordinates, depending upon the temperature of the solution:

20C. 0.5 to 7 moles per liter 35 C. 0.75 to 6 moles per liter 50 C. 1.25 to 6 moles per liter 55 C. 1.5 to 6 moles per liter By operating the currentless plating process in this manner, excellent copper coatings are obtained even when the ferrous metal surface is super-refined steel.

More specifically, in the practice of the method of the present invention, the ferrous metal surface to be plated is brought into contact with an aqueous acidic solution which consists essentially of copper ions, hydrogen ions, and fluoride ions and is free of inhibitors and which contain the hydrogen ions and fluoride ions within the limits set forth hcreinabove, which limits are a function of the temperature of the coating solution. It is to be appreciated, that in referring to the fluoride ion concentrations, within these limits, it is intended to denote that it is the concentration of the fluoride ions which are not bound in complexes, while the reference to the hydrogen ion concentrations within these limits is intended to denote the quantity of hydrogen ions which can be determined by titration, such hydrogen ions being either dissociated or nondissociated in the solution.

Although, as indicated above, the concentration of both the hydrogen ion and fluoride ions in the coating baths of the present invention are important and should be within the limits which have been indicated, the effect of the copper ion concentration on the bath performance has not been found to be as great. Accordingly, any copper ion concentration in the bath which will produce the desired copper plating on the metal surfaces treated may be used although, preferably, the copper ion concentration will be from about 5 to 60 grams per liter, calculated as CuSO,-5H,O.

Additionally, the plating baths of the present invention desirably also contain nitrate and/or sulfate and/or chloride ions. Generally, it is preferred that these ions be introduced into the coating bath as the anions of compounds containing the copper or hydrogen cation. Thus, the coating baths of the present invention may be formulated by using copper sulfate or copper nitrate as the source of copper ions, nitrate ions and/or sulfate ions, and sulfuric acid, hydrochloric acid, or nitric acid, as the source of hydrogen ions, chloride ions, sulfate ions, or nitrate ions. Additionally, the fluoride ions are desirably introduced into the solution as hydrogen fluoride, thus providing a source of both hydrogen ions and fluoride ions. It is to be appreciated, however, that other compounds containing these ions may also be used in formulating the plating solutions of the present invention, provided such compounds are water soluble and do not contain anions or cations which are detrimental to the coating bath or have an adverse effect on the copper plating obtained. Typical of such compounds which may be used are the alkali metal compounds, such as sodium fluoride, sodium sulfate, sodium nitrate and the like. In each instance, of course, the specific compounds used in formulating the plating baths will be chosen so that the resulting bath contains the hydrogen ions and fluoride ions in the indicated amounts for the particular bath temperature which is to be used.

It is believed that the suitability of the treating solutions of the present invention are based upon the fluoride ion content of the solution in conjunction with the definite functional temperature relationship of the hydrogen ion content. It is further believed that these factors, when the plating bath is used on super-refined steel, overcome the passivity of the super refined steel, thus making possible the formation of a satisfactory copper coating on the surface. By the addition of the various inhibitor materials which have been heretofore disclosed in the art, this effect is eliminated so that only solutions without these inhibitors will deposit a copper plating on superrefined steel.

in this regard, in referring to super-refined steel, it is intended to include those rust and acid resistant super alloys which contain at least about 13 percent of chromium and/or nickel. Such alloys have a low carbon content, typically less than about 0.1 percent, and may also contain other elements, such as molybdenum, titanium, and the like. While the present process and coating solutions may be used to form satisfactory copper coatings on various ferrous metal surfaces, the advantages of the present invention become particularly apparent when it is used in the treatment of the super-refined steels, which steels have not, heretofore, been capable of being coated with the currentless copper plating solutions of the prior art.

Referring now to the drawing which is attached hereto and forms a part hereof, this is a phase diagram showing the hydrogen ion and fluoride ion concentrations which must be maintained in the coating baths of the present invention under various temperature conditions. In this diagram, the fluoride concentration, given in moles per liter, is the ordinate while the hydrogen ion concentration, given in moles per liter, is the abscissa for temperatures of C., 35 C., 50 C., and 55 C. It is found that those copper coating compositions in which the concentration of hydrogen and fluoride ions are within the areas bordered by the heavy lines will produce light colored, satisfactory platings. in contrast, however, those compositions in which the hydrogen and fluoride ion concentrations are outside of these areas, at best, produce dark colored coatings which may be at least partially removed by rubbing and, in some instances, will produce no copper deposition at all. Thus, in order to obtain a satisfactory copper plating in accordance with the process of the present invention, it is necessary to maintain the coating baths conditions which are shown in the accompanying drawing. It is to be appreciated, however, that the temperatures used in the treating process may be between or even below or above the limits which are expressly stated in the drawing, provided that the concentrations of the hydrogen and fluoride ions are such as those which may be calculated from the phase diagram in the drawing.

As is seen from the phase diagram, the lower treatment temperatures are, generally, more desirable, with treatment temperatures at about room temperature being particularly suitable. As the phase diagram indicates, at these lower treatment temperatures, the concentration ranges for the bath components are not as narrow as is the case when higher treatment temperatures are used. Thus, it can be seen that when the lower treating temperatures are used, there is a wider range of component concentrations which will produce satisfactory results so that a less stringent control on the bath concentration is necessary than when operating at the higher temperatures. Thus, is has been found that at operating temperatures above about 70 C., the hydrogen and fluoride ion concentrations must be maintained between such narrow limits that it becomes very difficult to obtain satisfactory copper plating with the operating control conditions which prevail in many commercial plating operations. Additionally, it has been found that at high operating temperatures, it is sometimes difficult to obtain a satisfactory, adherent copper coating. Accordingly, the use of such higher operating temperatures is generally not preferred and it is desirable that the method of the present invention be carried out at operating temperatures from about room temperature, e.g., about 20 C., up to about 70 C. with the lower temperatures in this range being most preferred.

In carrying out the process of the present invention, the copper plating bath is formulated so as to contain the desired components in the amounts which have been indicated hereinabove. This aqueous acidic copper coating bath is then brought into contact with the ferrous metal surface, such as a surface of super refined steel, for a period sufficient to effect the formation of the desired copper coating on the metal surface. Although various contacting techniques may be used, such as spraying, flooding, immersion, or the like, immersion contacting techniques are generally preferred. Desirably, prior to contacting the ferrous metal workpiece with the plating solution, the workpiece is subjected to suitable pretreating operations, such as degreasing, pickling and the like. Thereafter, the copper plating bath is brought into contact with the workpiece and maintained until the desired copper coating is obtained. Typically, the contact times will be from about 15 to 60 minutes, although other suitable contact times may also be used which will produce a satisfactory coating.

In this manner, a copper deposit, typically having a coating weight of from about 5 to 30 grams per square meter, will be produced on the metal surface treated. Obviously, variations in the thickness of the coating may be obtained by shortening or lengthening the duration of the treatment. By operating in this manner, there is obtained currentless deposition of copper on the ferrous surfaces treated, which copper coating is generally light-colored and adherent, and may be fonned with equal ease on various ferrous surfaces, including surfaces of super-refined steel.

In order that those skilled in the art may better understand the present invention and the manner in which it may be practiced, the following specific examples age given. in these examples, unless otherwise indicated, temperatures are in degrees centigrade and parts and percents are by weight.

EXAMPLE I In a wire drawing installation, super-refined steel wires having the following composition:

Carbon 0.05%

Chromium l8 to l9% Nickel 9 to I01:

Molybdenum 2 to 2.2% Titanium 0.1%

were pickled in hydrochloric acid, rinsed in cold water and subsequently immersed into an aqueous acidic copper plating solution containing 17.5 grams per liter CuSO,5-H,O

3.45 grams per liter HF 54.4 grams per liter H 80, The solution was agitated by means of compressed air which was fed into the bath. After a 30-minute treatment time, the wires were taken out of the bath, rinsed with cold water and dried. Upon examination, all of the wires were found to have a light-colored, uniform copper coating of very good hardness and the coating weight was found to be 18 grams per square meter.

EXAMPLE 2 Super-refined steel wires of the quality given in the preceding example were treated in the same copper plating solution, using a treatment temperature of 20 C. and immersion time of 20 minutes. After removing the wires from the treating solution, rinsing them with cold water and drying, the wires were found to have a light-colored uniform copper coating of excellent hardness with a coating weight of 5 grams per square meter.

EXAMPLE 3 Super-refined steel wires of the quality set forth in example 1 were pretreated as in that example and then immersed for 20 minutes at a temperature of 20 C. in a copper plating bath having the following composition:

58.0 grams per liter CuSo,-SH,0

34.5 grams per liter Hf 54.5 grams per liter H,SO,

|0l0lz 0020 After removing the wires from the solution, rinsing and drying them, a light colored uniform copper coating of good hardness was obtained having a coating weight of 25.3 grams per square meter.

EXAMPLE 4 F- concentration, mol/l.

H+ concentration, moi/l.

Temperature, C. Evaluation of copper plating Light colored, adherent. Dark, rubs ofi. 50 Do. Do. Liglg colored, adherent.

0. Dark, rubs off.

0. Light colored, adherent.

D0. Dark colored, adherent EXAMPLE 5 A copper plating solution was formulated containing 30 grams per liter CuSlhSl-LO grams per liter NaCl 55.2 grams per liter H,S0,

0.4 grams per liter inhibitor in one instance, anhydrofonnaldehyde aniline pyridine was used as the inhibitor and in the second instance quinine was used. Super refined steel wires, as disclosed in example 1 were precleaned and treatedwith this solution in accordance with the procedure of that example, the treatment being carried out at a temperature of 66 centigrade for a period of 5 minutes. in each instance, no copper plating was obtained on the steel wire.

This procedure was again repeated with the exception that in both of the treating solutions used the sulfuric acid concentration was increased to 250 grams per liter and the sodium chloride was replaced with 24 grams per liter of sodium fluoride. Here again, using these solutions, no copper deposition was obtained on the super refined steel wires treated.

From the above results, it is seen that when operating in accordance with the method of the present invention, excellent copper coatings are obtained on the ferrous surfaces treated, even where these surfaces are of super refined steel, which. surfaces cannot be coated with the conventional plating solutions containing inhibitors. it is further found that by plating, the ferrous surfaces in accordance with the method of the present invention, the copper plating formed facilitates the cold-forming of these ferrous surfaces.

While there have been described various embodiments of the invention, the compositions and methods described are not intended to be understood as limiting the scope of the invention as it is realized that changes therewithin are possible and it is further intended that each element recited in any of the following claims is intended to be understood as referring to all equivalent elements for accomplishing substantially the same result in substantially the same or equivalent manner, it being intended to cover the invention broadly in whatever form its principle may be utilized.

What is claimed is:

l. A process for producing a copper plating on ferrous metal without the use of current which comprises contacting a super-refined steel surface to be coated with an aqueous acidic solution consisting essentially of copper ions, hydrogen ions and fluoride ions, which solution is free of inhibitors, and maintaining the solution in contact with the surface until the desired copper coating is obtained, wherein the concentration of the fluoride ions is maintained within the limits given in the figure of the drawing as a function of temperature and delineated by the following coordinates:

20 C. 0.] lo 4 moles per liter 35 C. CH to 2.8 mole: per liter 50 C. 0.1 to l.3 moles per liter 55 C. 0.1 to 0.8 mole: per liter and the hydrogen ion concentration is maintained within the limits given in the figure of the drawing as a function of temperature and delineated by the following coordinates:

20C. 0.5 to 7 moles per liter 35 C. 0.75 to 6 moles per lilcr 50 C. L25 to 6 moles per liter 55 C. L5 to 6 moles per liter.

2. The process as claimed in claim 1 wherein the coating solution contains from about 5 to 60 grams per liter of copper calculated as CuS0 -5H,0.

3. The process as claimed in claim 2 wherein the coating solution also contains at least one additional ion selected from nitrate, sulfate and chloride ions.

4. The process as claimed in claim 3 wherein the treatment of the surface is carried out at a temperature within the range of 20 to 70 degrees C.

S. The process as claimed in claim 4 wherein the treatment of the surface is carried out at a temperature of about 20 C.

U i I i i 

2. The process as claimed in claim 1 wherein the coating solution contains from about 5 to 60 grams per liter of copper calculated as CuS04.5H20.
 3. The process as claimed in claim 2 wherein the coating solution also contains at least one additional ion selected from nitrate, sulfate and chloride ions.
 4. The process as claimed in claim 3 wherein the treatment of the surface is carried out at a temperature within the range of 20 to 70 degrees C.
 5. The process as claimed in claim 4 wherein the treatment of the surface is carried out at a temperature of about 20 degrees C. 